A NEAR-INFRARED STUDY OF EMISSION-LINE GALAXIES

Abstract

ABSTRACT The near infrared (near IR) imaging technique in the J (1.25 μm), H (1.65 μm), K (2.2 μm) and L (3.5 μm) bands has been applied to study the stellar and non-stellar processes in two types of emission-line galaxies: starburst galaxies and Seyfert 2 galaxies. In the first part of this work, we have carried out a detailed study of the star formation (SF) history in a small sample of starburst galaxies selected from the UCM (Universidad Complutense de Madrid) survey. We have combined optical imaging (Gunn-Thuan r) and spectroscopy, and near IR imaging (JHK) imaging withpopulation synthesis models. These models, which account for the stellar component, have been complemented with the gas contribution in the form of continuum and emission lines produced by H and He. We have computed the time evolution of the equivalent widths (EW) of H emission lines (Hβ, Hα and Brγ), and optical--near IR (rJHK) photometric magnitudes for different assumptions for the initial mass function (IMF) and the star formation rate (SFR): instantaneous bursts and constant SF. The model results are used to investigate the SF processes in a sample of starburst galaxies. In the second part of this work, near-IR images (JHKL) of an optically selected sample of Seyfert 2 galaxies have been used to study their stellar and non-stellar components. Finally, we compare the hard X-rays (2-10 keV), [O Iii]λ 5007 and L-band properties of low-redshift PG (Palomar-Green) quasars, Seyfert 1s and 2s to infer the torus induced reddening in the latter.